<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    
        #box {
            width: 200px;
            height: 200px;
            background-color: aqua;
        }
    </style>
</head>
<body>
    <div id="box"></div>

    <script>
    
        box.addEventListener('click', function() {
            this.style.backgroundColor = 'red';
        });
        
    </script>
</body>
</html>